1. Field of the Invention
The present invention relates to a field of semiconductor integrated circuit (IC) manufacturing, and more specifically, to an apparatus for and a method of adjusting and controlling illumination in an imaging system.
2. Discussion of Related Art
Integrated Circuit (IC) devices may be fabricated in and over a substrate, such as a wafer, that may include a semiconductor, such as silicon. Various types of materials may be added to, or removed from, the wafer during processing. The materials may include an insulator, such as silicon oxide, or a conductor, such as copper.
Certain materials may be added onto the wafer by processes, such as physical vapor deposition, chemical vapor deposition, and electroplating. Other materials already on the wafer may be modified by processes, such as thermal processing, oxidation, and ion implantation. Yet other materials also on the wafer may be removed by processes, such as wet etching, dry etching, and chemical mechanical polishing (CMP).
As desired, photolithography may be used so that materials may be added or removed selectively from the wafer. For each layer of the IC device, a pattern of features must be transferred accurately from a mask template onto the wafer. Critical features in the pattern must be printed precisely and uniformly with a desired shape, size, separation, orientation, and location.
In order to satisfy product requirements for performance and reliability, critical parameters of the IC device must be measured during fabrication on the wafer. A critical dimension (CD) refers to a smallest lateral dimension, or width, of a feature or a smallest lateral separation between adjacent features that can be printed with good fidelity. Control of the CD may be compromised if an illumination is not correctly adjusted and properly controlled in an imaging tool used for the photolithography.
Thus, a need exists for an apparatus for and a method of adjusting and controlling illumination in an imaging system.